Recovery of tocopherols

ABSTRACT

Starting from a mixture containing tocopherol, fats and/or fat derivatives, more particularly fatty acids, and optionally sterol and/or sterol derivatives, the free fatty acids present in the mixture are esterified with an alcohol. The mixture is then transesterified with an alcohol in the presence of a basic catalyst. After the transesterification, the excess lower alcohol is distilled off from the reaction mixture. The transesterification catalyst and the glycerol present, if any, are removed and the fatty acid alkyl ester is distilled off from the mixture. Distillation of fatty acid alkyl esters can be accomplished with a packed column in sequence with a wiped film evaporator. The simultaneous recovery of tocopherol and sterol is possible. Tocopherols and sterols can be separated by the crystallization of sterols from a blend of organic solvents.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. Ser. No.08/531,366, filed Sep. 20, 1995, now U.S. Pat. No. 5,616,735 which is acontinuation of U.S. Ser. No. 08/180,592, filed Jan. 13, 1994, nowabandoned, which is continuation of U.S. Ser. No. 08/103,628, filed Aug.6, 1993, now abandoned.

FIELD OF THE INVENTION

This invention relates to a process for recovering tocopherol and,optionally, sterol from a mixture containing tocopherol, fats and/or fatderivatives, more particularly fatty acids, and optionally sterol and/orsterol derivatives.

Tocopherol compounds occur in many vegetable and animal oils and arealso referred to as vitamin E. The vitamin E relates to thephysiological effect of these food ingredients.

There are 8 naturally occurring substances with vitamin E activity. Theyare derivatives of 6-chromanol and belong to two groups of compounds.The first group is derived from tocol and carries a saturatedisoprenoidal side chain containing 16 carbon atoms. This group includesalpha-, beta-, gamma-, and delta-tocopherol. The compounds differ intheir degree of methylation at the benzene ring of the tocol.Alpha-tocopherol is the substance with the strongest biological vitaminE effect and the greatest technical and economical importance. It is thedominant tocopherol in human and animal tissue.

The second group of substances with vitamin E activity are thederivatives of tocotrienol. They differ from the other tocopherolhomologs in the unsaturated isoprenoidal side chain containing 16 carbonatoms. The naturally occurring tocoenols also show vitamin E activityand are normally isolated from their natural sources together with thesaturated tocopherol homologs in the recovery of vitamin E. In thecontext of the present invention, the name "tocopherol" is also intendedto encompass these tocopherol homologs, i.e. tocopherol are found invegetable oils, such as wheat-germ oil, corn oil, soybean oil and palmkernel oil. However, tocopherol is also found in other vegetable oils,for example in safflower oil, peanut oil, cottonseed oil, sunflower oil,rapeseed oil, palm oil and other vegetable oils.

The natural plant oils contain only small quantities of tocopherol.Concentration is undesirable for commercial applications. In addition,impurities are supposed to be removed to enhance the antioxidizingeffect and vitamin E activity. Accordingly, the most important naturalsources of tocopherol are not the vegetable oils themselves, but ratherthe steam distillates--also know as steamer distillates--obtained in thedeodorization of vegetable and animal oils. Although the tocopherols areobtained in concentrated form, they are mixed with sterol and sterolesters, free fatty acids and triglycerides. The distillate from thedeodorization of soybean oil is particularly interesting. The particularsuitability of soybean oil as a source of tocopherols is mentioned, forexample, in Fat Sci. Techol., Vol. 91, 1989, pages 39 and 41 in acomparison of the deodorization distillates of soybean oil and rapeseedoil. The soybean oil steamer distillate contains approximately 10%(maximum) by weight mixed tocopherols and the same amount of sterolswhich are predominantly present in their ester form.

There are various known processes for the concentration of tocopherol,namely esterification, saponification and fractional extraction. Thus,according to DE 31 26 110 A1, tocopherol concentrates are obtained fromsecondary products of the deodorization of oils and fats byesterification of the free fatty acids present therein by addition of analcohol or by removal of the free fatty acids from the distillates bydistillation, after which these products are subjected to hydrogenationand subsequently to solvent fractionation to extract the tocopherols.Another process for concentrating tocopherol is known from the samedocument. In this process, the deodorization distillates are subjectedto transesterification with methanol and the fatty acid methyl estersare distilled off. The residue is concentrated by moleculardistillation.

In another process known from EP 171 009 A2, the tocopherol-containingmaterial is contacted with a sufficient quantity of a polar organicsolvent which dissolves the tocopherols, but not the impurities. Thepolar phase enriched with tocopherol is separated off and the tocopherolis recovered therefrom.

It is also known that the tocopherols can be separated by adsorptiononto basic anion exchangers. This variant is possible if the mixturecontains little, if any, fatty acid. The sterols, glycerides and otherneutral or basic substances are not adsorbed (Ulmanns Enzykldopadie derTechnischen Chemie, 4th Edition, Vol. 23, 1984, page 645).

It is also known that sterols can be separated from tocopherols byfractional crystallization after concentration. In this process,tocopherol passes into solution and sterol crystallizes out. Tocopheroland sterol can also be separated by distillation, except that in thiscase the sterol is at least partly destroyed. Accordingly, two usefulproducts are obtained after the separation of tocopherol and sterol.

Known processes for the recovery of tocopherol and, optionally, sterolare attended by various disadvantages.

The extraction processes often have to be adapted to the startingmixture because the impurities present therein have a considerablebearing on extraction, and the desired useful products, tocopherol andsterol, do not always pass into the desired phase with the sameextraction process and different starting mixtures. In addition, knownextraction processes use physiologically unsafe solvents.

Ion exchangers have a specific effect on the starting material, requiredthorough preliminary purification of the mixture and do not allowtocopherol and sterol to be simultaneously concentrated.

In a variant described in DE 31 26 110 A1, tocopherol is subjected tomolecular distillation or to steam distillation after esterification ofthe free acids with polyhydric alcohols in order to obtain a distillatehaving a high tocopherol content. However, the process step of moleculardistillation is uneconomical on an industrial scale while steamdistillation involves exposure to relatively high temperatures which atleast partly destroys the sterols. In the latter case, therefore, onlythe thermally more stable tocopherol can be obtained in high yields.

Accordingly, the problem addressed by the present invention was toprovide a process for the recovery of tocopherol and, optionally, sterolwhich would be applicable to many different starting mixtures and whichwould not use any toxicological or ecologically unsafe solvents, wouldnot involve exposure to high temperatures, would give high yields andwould be economically workable on an industrial scale. In addition, thesimultaneous recovery of tocopherol and sterol would be possible.

SUMMARY OF THE INVENTION

This invention relates to various steps in the recovery of tocopherols,typically from sources in which the tocopherols are in a mixtureadditionally comprising fatty compounds (e.g. fatty acids and/or fattyglycerides) and sterols (e.g. free sterols and/or steryl fatty acidesters). The various steps of the processes of the invention can beoutlined as follows. As will be appreciated, the following outline dealswith two alternative pre-esterification/transesterification processes,followed by a distillation process (which serve to remove fattycompounds from the mixture, e.g. as lower alkyl fatty esters), and acrystallization process (which serves to separate sterols fromtocopherols).

I. Pre-Conversion and Removal of Fatty Compounds

A. Pre-esterification/Transesterification

1. Pre-Esterification/Transesterification with methanol recovery

In one aspect, this invention relates to a process for recovery oftocopherols from a mixture comprised of fatty acids and tocopherols,said process comprising:

pre-esterifying free fatty acids present in said mixture with a loweralcohol (preferably a member selected from the group consisting ofprimary and secondary mono-alkanols having less than five carbon atoms),

transesterifying fatty acid esters present in said mixture with a loweralcohol in the presence of a basic catalyst, and

distilling excess lower alcohol from the product of saidtransesterification (and preferably recycling at least a portion of saiddistilled methanol to said transesterifying step),

washing the product of said transesterification (preferably withessentially pure water) to remove said basic catalyst and glycerolproduced by said transesterification,

distilling fatty acid alkyl esters from said mixture after inactivation(e.g. neutralization or removal) of said basic catalyst.

In preferred embodiments, the process additionally comprises one or moreof the following steps of employing a polymer-supported acid catalyst insaid pre-esterification and employing a mixture comprised of both one ormore tocopherol compounds and one or more sterol compounds (preferablycomprised of one or more sterol esters that are transesterified in thepre-esterification and/or said transesterification steps) and recoveringfrom said mixture one or more tocopherol compounds separate from one ormore sterol compounds after said distillation of fatty acid alkylesters.

In a related aspect, this invention relates to a process comprising:

free fatty acids present in the mixture are esterified with a loweralcohol, preferably methanol,

the mixture is subsequently transesterified with the lower alcohol inthe presence of a basic catalyst,

the excess lower alcohol is distilled off from the reaction mixtureafter the transesterification,

the transesterification catalyst and optionally the glycerol present areremoved, more particularly by washing,

the fatty acid alkyl ester is distilled off from the mixture, moreparticularly after removal of the transesterification catalyst, and

if desired, tocopherol and sterol are separated by methods known per se.

2. Pre-esterifying with Higher Alcohol Land Transesterifying with LowerAlcohol)

In another aspect, this invention relates to a process for recovery oftocopherols from a mixture comprised of fatty compounds and tocopherols,said process comprising:

pre-esterifying free fatty acids present in said mixture with a higheralcohol (preferably a member selected from the group consisting ofprimary and secondary mono-alkanols having at least five carbon atoms)and removing by-product water by volatilization thereof,

transesterifying fatty acid esters present in said mixture with analcohol, preferably a lower alkanol, in the presence of a basiccatalyst, and

distilling alkyl fatty acid esters from said mixture afterincapacitation (e.g. neutralization or removal) of said basic catalyst.

In preferred embodiments, the process additionally comprises one or moreof the following steps, preferably each of the following steps in theorder set forth below:

employing a higher alcohol that is moderately volatile (and preferablyessentially immiscible with water) such that a portion of said alcoholis distilled with said by-product water (and is preferably separated bygravity from said by-product water after condensation of said higheralcohol) and recycling higher alcohol after its distillation (andpreferably after separation from by-product water),

distilling excess lower alcohol from the product of saidtransesterification,

washing the product of said transesterification to remove said basiccatalyst and glycerol produced by said transesterification,

distilling higher alcohol from the product of said transesterificationas a fraction separate from said alkyl fatty acid esters, and

employing a mixture comprised of both one or more tocopherol compoundsand one or more sterol compounds (preferably comprised of one or moresterol esters that are transesterified in the pre-esterification and/orsaid transesterification steps, preferably at least 50% by weight of thesterol esters are converted to free sterols, more preferably at leastabout 80%, typically from about 85% to about 95%) and recovering fromsaid mixture one or more a tocopherol compounds separate from one ormore sterol compounds after said distillation of fatty acid alkylesters.

B. Alkyl Fatty Ester Distillation

1. Distillation with Packed Column

In another aspect, this invention relates to an evaporative process forthe separation of fatty acid lower alkyl esters from a mixtureadditionally comprising tocopherols and sterols, said processcomprising:

introducing said mixture into a moderately heated zone of elevatedtemperature and reduced pressure, said zone containing multiple packingelements in an essentially continuous bed, said elevated temperature andreduced pressure being effective to provide within said continuous bed afirst vapor phase enriched with respect to said mixture in alkyl fattyacid esters and a first liquid phase enriched with respect to saidmixture in tocopherols and sterols;

removing liquid phase enriched in tocopherols and sterols from saidcontinuous bed at a point gravitationally below the point ofintroduction of said mixture into said heated zone;

removing vapor phase enriched in alkyl fatty acid esters from saidcontinuous bed at a point gravitationally above the point ofintroduction of said mixture into said heated zone;

applying said liquid phase enriched in tocopherols and sterols as a filmto a highly heated surface in proximity with a zone of reduced vaporpressure to provide a second vapor phase enriched with respect to saidliquid phase in alkyl fatty acid esters and a second liquid phaseenriched with respect to said first liquid phase in tocopherols andsterols as a film in contact with said heated surface;

removing said vapor enriched in alkyl fatty acid esters from said zoneand removing said film of said second liquid phase from said heatedsurface, said removing of said film being accomplished by mechanicalagitation; and

removing said second liquid phase from proximity with said zone ofreduced vapor pressure to an environment of essentially ambienttemperature.

In certain embodiments, the mixture is pre-heated and pre-distilled at arelatively low temperature (i.e. low relative to the moderatetemperature of the packed column) as a film from a continuous heatedsurface and the liquid phase film is removed by gravity flex down saidheated surface, for example as in a falling film evaporator.

2. Partial Stripping with Evaporator

In another aspect, this invention relates to the separation of a portionof the alkyl fatty esters from a mixture additionally comprisingtocopherols and sterols, said process comprising:

applying said mixture as a film to a heated surface in proximity with azone of reduced vapor pressure to provide a vapor phase enriched withrespect to said liquid phase in alkyl fatty acid esters, said vaporphase being essentially free of tocopherols and sterols, and a liquidphase enriched with respect to said first liquid phase in tocopherolsand sterols as a film in contact with said heated surface;

removing said vapor enriched in alkyl fatty acid esters from said zoneand removing said film of said liquid phase from said heated surface(said removing of said film preferably being accomplished by mechanicalagitation); and

removing said liquid phase from proximity with said zone of reducedvapor pressure to an environment of essentially ambient temperature,(preferably wherein said liquid phase is collected in an amount of fromabout 30% to about 60% by weight of said mixture).

II. Sterol Crystallization with Mixed Solvents of Differential Polarity

In another aspect, this invention relates to a method of separating oneor more tocopherol compounds from one or more sterol compoundscomprising:

dispersing a mixture of one or more tocopherol compounds and one or moresterol compounds, said mixture being essentially free of higher fattyacid compounds, in a solvent mixture comprised of a major amount of alow polarity organic solvent, said low polarity organic solvent beingselected from the group consisting of organic hydrocarbon solvents andoxygenated organic hydrocarbon solvents, and a minor amount of a highpolarity organic solvent (and preferably with a minor amount of water),

maintaining the resulting dispersion, preferably at a reducedtemperature, to produce a liquid phase enriched in tocopherol compoundsand a solid phase enriched in sterol compounds, and

separating said liquid phase enriched in tocopherol compounds from saidsolid phase enriched in said sterol compounds.

In preferred embodiments, the process further comprises, prior to saiddispersing, esterifying with an alcohol fatty compounds in a mixturecomprised of fatty acids, fatty glycerides, tocopherols and sterols,distilling at least a major proportion of the fatty acid alkyl estersproduced by said esterifying to produce said mixture of one or moretocopherol compounds and one or more sterol compounds.

DETAILED DESCRIPTION OF THE INVENTION

The following description will deal with the various aspects of theinvention in the order presented in the outline above.

The starting material for the process of the invention is a mixturewhich contains fatty compounds and sterol compounds in addition totocopherols. A major advantage of the process according to the inventionis that it can be applied to various mixtures containing tocopherol and,optionally, sterol. In particular, however, it is of advantage to startout from soybean oil steamer distillate which is obtained by steamdistillation of crude soybean oil as the first stage of thedeodorization process. Oil deodorization is discussed in Bailey'sIndustrial Oil and Fat Products, vol. 3, pp. 127-165, (John Wiley &Sons, Inc. New York, N.Y., 1985), the disclosure of which isincorporated herein by reference. The distillates contain approximately20% sterol, 8% tocopherol, 20% free fatty acids and, as its principalconstituent, triglycerides (Ullmans, Ioc. cit.).

However, steamer distillates of other oils, for example rapeseed oildistillates, can also be processed by the process according to theinvention.

The process according to the invention is by no means limited in itsapplication to steamer distillates of vegetable oils and fats. It mayalso be applied with advantage to tall oil. Tall oil is, economically,one of the most important secondary products of the cellulose sulfateprocess used in papermaking. It is obtained by acidification of thesodium salt mixture or resinic and fatty acids formed in this process.Tall oil is a natural mixture of resinic acids of the abietic acid type,saturated and unsaturated fatty acids and fatty acid esters and anunsaponified fraction. In addition to higher alcohols and hydrocarbons,the unsaponifiable fraction also contain sterols.

Other mixtures containing tocopherol may also be worked by the processaccording to the invention, for example the residue obtained in theproduction of rapeseed oil methyl ester which also contains sterols andsterol esters.

Pre-Esterification/Transesterification

Lower Alkanol Use and Recovery

In a first step, the free fatty acids present in the starting mixtureare reacted with a lower alcohol to form fatty acid alkyl ester, moreparticularly fatty acid methyl ester, in order to rule out asaponification reaction with the transesterification catalyst used inthe next step. In the case of mixtures with no free fatty acids, thisfirst step may be omitted. In the following process step,transesterification, the sterol fatty acid ester is reacted to steroland fatty acid methyl ester. The partial glycerides and triglyceridesreact to form glycerol and fatty acid methyl ester. The tocopherolpresent in the mixture does not react. In many cases, not onlytocopherols, but also tocopherol esters are present in the startingmixture, for example in the soybean oil steamer distillate with 0.5%(maximum) by weight. In this step, the esters are converted intotocopherols. For the next process step, removal of the excess loweralcohol by distillation, it is of particular advantage if a short-chainalcohol, more particularly methanol, has been used in the precedingsteps. In this way, exposure to high temperatures can be minimized.Before removal of the alkyl fatty acid ester by distillation, it isadvisable not only to separate the glycerol formed in thetransesterification step from triglycerides present, if any, but also toremove the transesterification catalyst. The catalyst is largely presentin the form of alkali metal soap which could be problematical duringdistillation and could lead, for example, to an increase in the boilingpoint. A highly concentrated tocopherol/sterol mixture is obtained afterremoval of the fatty acid alkyl ester. The tocopherol and sterol in thismixture can be separated from one another by methods known per se, forexample by crystallization.

In one preferred embodiment of the process according to the invention,the fatty acids are esterified in the presence of a strongly acidic ionexchanger, more particularly present in a fixed-bed reactor, attemperatures in the range from 60° to 100° C. and more particularly attemperatures in the range from 65° to 70° C. The distinctly smaller lossof tocopherol through its solubility in methanol than occurs in theremoval of the fatty acids by distillation was both advantageous andsurprising. In the esterification of the fatty acids, the ratio of thevolume streams between steamer distillate and lower alcohol is between1.1 and 1.7 and preferably 1.4. The residence time in the fixed-bedreactor is 1 to 2 hours and preferably 1.6 hours. These figures apply tothe free volume actually present. In esterification, the fatty acidspresent in the mixture are reacted to fatty acid alkyl ester at theactive centers of the strongly acidic ion exchanger. The use ofpolymer-supported catalysts is discussed in the Encyclopedia of PolymerScience and Technology, vol. 2, pp. 708-729 (John Wiley & Sons, Inc.,1985), the disclosure of which is incorporated herein by reference.

After the reaction, the excess lower alcohol, i.e. generally methanol,is removed in a phase separator. The alcohol additionally contains thepredominant part of the water formed during the esterification.

The product is then transesterified in the presence of a basic catalyst,e.g. a lower alkoxide (preferably in a solution of the same loweralkanol, e.g. sodium methoxide in methanol.) Transesterificationreactions are discussed in Encyclopedia of Chemical Technology, vol. 9,pp. 306-308 (Kirk-Othmer, eds., John Wiley & Sons, Inc., New York, N.Y.,1980), the disclosure of which is incorporated by reference. After thetransesterification and the removal of the excess alcohol from thereaction mixture, the catalyst and any glycerol present are removed fromthe mixture. The catalyst is preferably neutralized before-hand byacidification with an inorganic acid (e.g. hydrochloric acid or sulfuricacid).

Pre-esterifying with Higher Alcohol

In an alternative aspect, this invention relates to a process forrecovery of tocopherols from a mixture comprised of fatty acids andtocopherols wherein free fatty acids present in said mixture arepre-esterified with a higher alcohol (preferably a member selected fromthe group consisting of primary and secondary mono-alkanols having atleast five carbon atoms) and water e.g. that produced by thepre-esterification, is removed by volatilization thereof. This processalso preferably includes the steps of transesterifying fatty acid esterspresent in said mixture with a lower alcohol in the presence of a basiccatalyst, and distilling fatty acid alkyl esters from said mixture afterincapacitation (e.g. neutralization or removal) of said basic catalyst.

The process preferably employs a higher alcohol that is moderatelyvolatile (and preferably essentially immiscible with water) such that aportion of said alcohol is distilled with said by-product water (and ispreferably separated by gravity from said by-product water aftercondensation of said higher alcohol) and recycling higher alcohol afterits distillation (and preferably after separation from by-productwater). For example, a monohydric alkanol (preferably a primary alkanolor secondary alkanol), having from about five to about fourteen(preferably six to ten) carbon atoms is preferred. Examples include amylalcohol, n-hexanol, 2-hexanol, n-heptanol, n-octanol, 2-ethylhexanol,n-nonanol, n-decanol, and 2-decanol, n-dodecanol (e.g. lauryl alcohol),n-tridecyl, and n-tetradecyl (e.g. myristyl alcohol).

In preferred embodiments, the process additionally comprises the stepsof:

distilling excess lower alcohol from the product of saidtransesterification,

washing the product of said transesterification to remove said basiccatalyst and glycerol produced by said transesterification,

distilling higher alcohol from the product of said transesterificationas a fraction separate from said fatty acid alkyl esters. This allowsfor the efficient recovery and, optionally, recycling of the lower andhigher alkanols.

Further, the process preferably employs as a starting material, amixture comprised of both one or more tocopherol compounds and one ormore sterol compounds (preferably comprised of one or more sterol estersthat are transesterified in the pre-esterification and/or saidtransesterification steps) and recovering from said mixture one or moretocopherol compounds separate from one or more sterol compounds aftersaid distillation of fatty acid alkyl esters.

A mixture of a higher alkyl alcohol and an acidic catalyst, e.g.p-toluenesulfonic acid (PTS), methanesulfonic acid, hydrochloric acid(HCI) or sulfuric acid, is introduced into a vessel. The reactants areheated and the esterification reaction is conducted at temperaturesufficient to distill from the mixture water produced by theesterification of free fatty acid, preferably between 100° C. and 130°C. Higher alkyl alcohol is present in the reaction mixture during theesterification, preferably in stoichiometric excess (with respect to thefree fatty acids, e.g. a ratio of about 1.5:1 to about 4:1, moretypically from about 2:1 to about 2.5:1, on a molar basis) to facilitateconversion of the free fatty acids to higher alkyl fatty acid esters.The acid catalyst is present in small amounts, e.g. 0.005% to about1.0%, typically 0.01% to about 0.2% and more typically 0.05% to 0.1%, byweight of the pre-esterified feed.

Because the higher alkyl alcohol is preferably moderately volatile (e.g.more volatile than the lower alkanols, but less volatile than thetocopherols, preferably less volatile than the alkyl fatty esters), aportion of thereof will be distilled with the water. Thus, it ispreferred to continuously introduce higher alkyl alcohol into thereaction vessel and to recover the evaporated higher alkyl alcohol bythe condensation. The by-product water of reaction and the higher alkylalcohol, are preferably sufficiently immiscible to allow a gravityseparation, e.g. by decantation, of water and higher alkyl alcohol.

The esterification reaction should be conducted for a time sufficient toreduce the free fatty acid concentration in the starting material to thedesired degree. It is preferred to conduct the reaction to the pointthat there will be minimal reaction of free fatty acid with the basiccatalyst used in the subsequent transesterification step. The reactionis typically conducted for a time sufficient to reduce the acid value ofthe product to less than one. When this value is reached, at least aportion (and preferably essentially all) of the excess higher alkylalcohol is distilled (to recover higher alkyl alcohol in a simpledistillation and reduce the potential inhibition of the subsequenttransesterification reaction with a lower alcohol), typically underreduced pressure. When the reaction and subsequent distillation iscompleted, the reaction mixture is cooled.

The pre-esterification reaction product is then transesterified,preferably with a lower alcohol, preferably a C₁ to C₄ mono-hydricalkanol, e.g. methanol, ethanol, n-propanol, isopropanol, n-butanol, ortert-butanol. The alcohol and a catalyst, such as potassium hydroxide,sodium hydroxide or sodium methoxide, are typically added to a reactionvessel. Alcohol is present in the reaction mixture during theesterification, preferably in stoichiometric excess of fatty esters inthe product, Typically, an amount of alcohol equal in mass to from about20% to about 80%, more typically about 50% to about 60%, with respect tothe mass of original tocopherol containing starting material is employedto facilitate conversion of the fatty esters (e.g. the higher alcoholfatty acid esters, glycerides, and fatty esters of sterols) to alkylfatty acid esters. There should be essentially no water present in thereaction medium during transesterification (e.g. less than 0.1% byweight) to avoid the formation of soaps. Thus, the pre-esterificationproduct should be dried, e.g. by air stripping or by use of an alkoxidecatalyst in sufficient excess to convert any water present to methanoland a hydroxide.

Transesterification is preferably conducted at a temperature between 50°C. and 100° C. and in reaction times of 10 minutes or more, e.g. 1 to 3hours. Typically, the vessel will be moderately pressurized (e.g. suchthat a reaction temperature of about 90° C. can be employed withsufficient methanol to maintain a liquid reaction phase). The reactionis conducted until the desired degree of transesterification isobtained, preferably until a major proportion (e.g. more than 50% byweight, typically at least about 90%) of the sterol fatty acid estersare transesterified to produce free sterols. The catalyst should then beneutralized with an essentially equal stoichiometric amount of acid,preferably anhydrous sulfuric acid (preferably no more than 2% by weightwater). The excess alcohol (and any now free higher alcohol) should thenbe distilled from the mixture (e.g. in a series of simple distillationof lower alcohol followed by simple distillation of higher alcohol)prior to optional treatment with a chelating chemical (such as ascorbicacid (vitamin C), phosphoric acid, maleic acid, citric acid or tartaricacid), followed by water washing (to remove glycerol and salts), andoptional nitrogen sparging and drying.

Distillation of Alkyl Fatty Acid Esters

The pre-esterification and transesterification steps performed aboveyield a mixture comprised of tocopherols, sterols and alkyl fatty acidesters. The alkyl fatty acid esters can be separated from the mixture asa distillate. The distillation should be accomplished in a manner suchthat unacceptable degradation of the tocopherols and/or sterols isavoided. Distillation is discussed in E. Hafslund, "Distillation",Encyclopedia of Chemical Technology, vol. 7, pp, 849-891 (Kirk-Othmer,eds. John Wiley & Sons, New York, 3d ed. 1979) and evaporation isdiscussed in F. Standiford, "Evaporation", Encyclopedia of ChemicalTechnology, vol. 9, pp. 472-493 (Kirk-Othmer, eds. John Wiley & Sons,New York, 3d ed. 1980), the disclosures of which are incorporated byreference.

Distillation of the alkyl fatty acid esters can be accomplished asdescribed in U.S. Pat. No. 5,190,618 (Top et al.), the disclosure ofwhich is incorporated by reference. In that patent, distillationequipment consists of a high heat-transfer distillation column, i.e. ahigh heat-transfer rate falling film distillation column, and distillatecollection system. The distillation process is continuous. Alkyl estersare distilled at high vacuum at below 10 mm of Hg (1333 N/m³) and at atemperature between 100° C. and 200° C. Distilled alkyl esters arecollected by condensation and discharged as a by-product. The retentiontime of the tocopherols and sterols in the distillation column is short,so that deterioration is minimal. More than one distillation cycle maybe practiced, but is clearly undesirable because of degradation of thebottoms, particularly the sterols (which tend to be particularlysusceptible to heat-induced degradation).

Distillation of alkyl fatty esters is, however, preferably conducted bya employing a packed distillation column at a moderate temperature (i.e.lower than the reboiler evaporator temperature) and an evaporator at ahigher temperature (i.e. higher than the temperature to which the packedcolumn is heated) in which the liquid phase will have minimal residencetime, such as in a wiped-film evaporator. This distillation ispreferably accomplished by introducing a pre-heated liquid intoessentially the mid-point of a packed column, removing the bottoms ofthe packed column to a wiped film evaporator, and removing the bottomsfrom the wiped film evaporator to a zone of ambient temperature. Thevapor phase from the wiped film evaporator re-enters the packed columnthrough the bottom of the column. The packed column will typically beconfigured to provide 5-12 theoretical stages or plates above the pointof introduction and 5-12 below theoretical stages or plates below thepoint of introduction and will typically be operated with a temperatureand pressure at the top of the column of 120° C. to 150° C. and 0.1 mbarto 3 mbar and at the bottom of the column at 180° C. to 220° C. and 3mbar to 9 mbar, with a reflux ratio of 0.4 to 0.6 and distillate as apercentage of feed (based on weight) of 60% to 80%. This column is thusoperated at a temperature that is lower than the temperature employed inthe wiped film evaporator reboiler.

The wiped film evaporator will typically be operated as a reboiler forthe packed column with a temperature of 200° C. to 300° C., typically at260° C. and pressure of 50 to 90 mbar. The mechanical agitation of thefilm within the wiped film evaporator will ensure that the mixture oftocopherols and sterols will have a short residence time at the hightemperatures employed. This will minimize degradation of the tocopherolsand sterols and thus enhance the overall yields. The mechanicalagitation of the film will preferably ensure that contact of anyparticular portion of the mixture of tocopherols and sterols with theheat exchanger surface is essentially instantaneous with removal thereoffrom such contact (e.g. by bringing such portion to the surface of thefilm in contact with the reduced pressure atmosphere maintained withinthe evaporator where evaporative cooling will lower the temperature ofthat portion of the mixture). Of course, such portion of the film canagain come in contact with the surface of the heat exchanger, but willagain be removed from contact therewith by the mechanical agitation.Further, the mechanical agitation will act to shorten the overallresidence time in the evaporator of any particular portion of themixture.

The distillation sequence described above will typically effect anessentially complete separation of alkyl fatty acid esters from theadmixture with tocopherols and sterols. For example, the ultimatebottoms will contain less than 1%, typically less than 0.5%, of alkylfatty acid esters. However, it may be desirable under certaincircumstances to perform only a partial removal of alkyl fatty estersfrom such a mixture. Such a partial removal is advantageouslyaccomplished by the process described above, but dispensing with the useof the packed column, i.e. by the use of a falling film evaporator or awiped film evaporator. However, the heat exchanger surface willtypically be heated to a lower temperature, e.g. 100° C. to 200° C. fora falling film evaporator and 150° C. to 250° C. for a wiped filmevaporator, to allow for a longer residence time.

The partial stripping will be particularly advantageous if used toremove a portion of the alkyl fatty esters from a mixture wherein theweight ratio of alkyl fatty esters to total weight of tocopherols andsterols combined ranges from about 1.5:1 to about 5:1. The strippingwill typically be effective in removing from about 30% to about 60% ofsaid mixture (i.e. the esterified feed) as alkyl fatty esters in whileremoving only nominal amounts of tocopherols and sterols, e.g. the alkylfatty esters will contain less than 5% by weight, typically less than 3%by weight, of tocopherols and sterols combined.

II. Sterol Crystallization with Mixed Solvents of Differential Polarity

The product of the distillation step will be enriched in tocopherols andsterols. The tocopherols and sterols can be separated from the mixtureby any of a variety of means, e.g. chromatographic separation based ondifferential solubility and/or adsorption or other interaction with asolid phase. Preferred, however, is a method in which the mixture isdispersed in a particular solvent system which facilitates the formationof a liquid phase enriched with respect to the mixture in tocopherolcompounds and a solid phase enriched with respect to the mixture insterol compounds and then physical separation of the liquid and solidphases. This can be considered a crystallization process.Crystallization processes are discussed in the Encyclopedia of ChemicalTechnology, vol. 7, pp. 243-285 (Kirk-Othmer, eds. John Wiley & Sons,New York, 3d ed. 1979), the disclosure of which is incorporated hereinby reference.

Of course, in the broadest sense, the mixture of tocopherols and sterolsmay be the product of other methods of separation of the fatty compoundsnormally found therewith in products of nature, e.g. by the aqueoussaponification of the fatty compounds followed by extraction of thetocopherols and sterols into an organic solvent. Preferably, however,the feed for the crystallization will be the product of a distillationof fatty acid alkyl esters. Without wishing to be bound by anyparticular theory, unless expressly set forth otherwise, it is believedthat the product of a distillation of fatty acid alkyl esters will havea composition that differs from the product of saponification andextraction in the nature and amounts of impurities and/or the identityand amounts of the tocopherols and sterols. For example, thedistillation product may well have greater amounts of impurities havinggreater water solubility such that these impurities remained with thefatty acid soaps in the aqueous phase during the extraction of thesaponification product. This difference in composition may thus causethe two different products to perform differently in a givencrystallization process.

The preferred method of separating one or more tocopherol compounds fromone or more sterol compounds of the mixture typically begins withdispersing a mixture of one or more tocopherol compounds and one or moresterol compounds, said mixture being essentially free of higher fattyacid compounds, in a solvent mixture comprised of a major amount of alow polarity organic solvent, a minor amount of a high polarity organicsolvent, and a minor amount of water.

In the broadest sense, the high polarity solvent will be an organicsolvent having a higher polarity (as measured for example by thedielectric constant of a pure liquid phase of the solvent at underambient conditions, e.g. room temperature) than the low polarity organicsolvent, and vice versa. The low polarity organic solvent willpreferably have a dielectric constant of less than about 25, morepreferably less than about 10, and the high polarity solvent willpreferably have a dielectric constant of more than about 25, morepreferably more than about 30. The dielectric constants of variousorganic solvents are set forth in the Handbook of Chemistry and Physics,pp. E-56 to E-58 (CRC Press, Inc., Cleveland, Ohio, 55th ed., 1974), thedisclosure of which is incorporated herein by reference. Typically, thelow polarity organic solvent will be a hydrocarbon solvent, i.e. oneconsisting solely of carbon and hydrogen atoms, or an oxygenatedhydrocarbon solvent, e.g. one consisting solely of carbon, hydrogen, andoxygen and having less than one oxygen atom per carbon atom.

Preferred low polarity organic solvents are the higher alkanes (ofsufficiently high molecular weight to form a practically handleableliquid phase, preferably straight-chain or branched-chain alkanes havingfrom 6 to 12 carbon atoms), e.g. hexane, heptane, n-octane, iso-octane,2,2,4-trimethylpentane, nonane, or decane; mono-ketones, e.g. acetone,2-butanone, or 2-octanone; mono-aldehydes, e.g. acetaldehyde orpropionaldehyde; mono-esters, e.g. ethyl formate or ethyl acetate;higher mono-hydric alcohols, e.g. n-propanol, iso-propanol, n-butanol,sec-butanol, n-hexanol, or 2-ethylhexanol. Preferred high polarityorganic solvents are low molecular weight, oxygenated hydrocarbons,preferably the lower alkanols such as methanol or ethanol. The solventblend will also preferably comprise a minor amount of water.

The solvent blend will be comprised of a major amount of the lowpolarity organic solvent, i.e. greater than 50% by weight of the solventblend, typically at least 80% and preferably from about 90% to 99.5%,e.g. from 92.0% to 99.0%. The high polarity organic solvent will bepresent in a minor amount, i.e. less than 50% by weight of the solventblend, typically less than 20% and preferably from about 0.5% to about10%, e.g. from 1.0% to 8.0%. Water is preferably present in an amountessentially equal to the high polarity organic solvent, e.g. in a ratioof high polarity organic solvent to water of from about 5:1 to 1:5, moretypically from about 3:1 to 1:3. Thus, preferred solvent blends arecomprised of from about 80% to about 99% by weight of a member selectedfrom the group consisting of higher alkanes, from about 0.5% to about20% of methanol or ethanol, and from about 0.5% to about 5% by weight ofwater.

The solvent blend and mixture of tocopherols and sterols are mixed toform what is initially a substantially homogeneous liquid phase. Themixture can be heated, e.g. to the atmospheric boiling point of thesolvent blend, to obtain a homogeneous liquid mixture. The ratio ofsolvent blend to feed mixture may vary, but will typically be from about10:1 to about 1:1, preferably from about 5:1 to about 3:1. The resultingmixture is maintained under conditions, typically at a reducedtemperature, to produce a liquid phase enriched in tocopherol compoundsand a solid phase enriched in sterol compounds. The temperature of themixture should be maintained below ambient, e.g. less than 25° C.,typically from about -40° C. to 20° C., more typically from about -25°C. to about 0° C. The mixture can be cooled from the temperature of itsdispersion to a reduced temperature at a variety of cooling rates, e.g.at relatively fast rates of about 80° C. per hour to about 120° C. perhour or relatively slow rates of about 2.5° C. to about 10° C. per hour.

The sterols crystallize or otherwise precipitate to form a solid phasethat can be physically separated from the liquid phase, e.g. byfiltering, centrifuging, or decanting. Preferably, the solid phasecollected will be at least 90% (typically at least 92%) by weightsterols with less than 5% (typically less than 2%) tocopherols and theliquid phase (mother liquor) will have a ratio of tocopherols to sterolsof greater than 5:1 (typically greater than 10:1 ). The mother liquor isenriched in tocopherols (with respect to the feed to thecrystallization) and can be further purified by distillation to collectmore highly purified tocopherols as distillate.

The following examples are intended to illustrate the invention withoutlimiting it in any way.

EXAMPLES Example 1

Esterification of the fatty acids

Part A

Soya steamer distillate having an acid value of 70 was introduced at avolumetric flow rate of 0.094 1/h together with 0.067 1/h methanol intoa 0.3 m long glass column charged with catalyst, namely a stronglyacidic macroporous ion exchanger resin (Lewatit K2631). The diameter ofthe column was 0.07 m. After a residence time of 1.6 h, the mixture wascollected in a glass vessel and decanted. Subsequent concentration byevaporation to separate the methanol/water mixture from the fatty phasewas carried out in vacuo. The acid value was subsequently determined at1.3, corresponding to a conversion of 98%, i.e. the loss of tocopherolwas negligible. Accordingly, the material has been deacidified for thefollowing transesterification step.

Part B

Deodorizer distillate having an acid value of 75 was charged to a batchreactor along with 0. 13% (by weight of the distillate) methanesulfonicacid and 30% (by weight of the distillate) of 2-ethylhexanol(approximately twice the amount of alcohol needed to esterify all freefatty acids in the distillate). The reaction medium was heated to 120°C. and water of reaction was removed through a reflux line atatmospheric pressure until most of the of the water of reaction had beenremoved (after about 3 hours), at which point the temperature of thereaction medium was raised to 135° C. and continued until an acid valueof 1.2 was achieved. Vacuum was then applied and the reaction medium washeated to 150° C. to remove excess 2-ethylhexanol. A similar batchpre-esterification which employed twice the concentration ofmethanesulfonic acid catalyst (i.e. 0.26% by weigh of the distillate)exhibited an increased reaction rate at the beginning of the reaction,but substantially the same reaction time. A second similar batchreaction, employing 0.13% (by weight of the distillate) methanesulfonicacid catalyst and 37.5% (by weight of the distillate) reduced thereaction time to substantially the same acid value to 100 minutes.

Example 2

Transesterification of the glycerides and sterol esters

Part A

The soya steamer distillate deacidified in the first step (acid valueapprox. 1) was contacted with methanol and the basic catalyst in a tubereactor. The reaction temperature was between 60° and 90° C. andpreferably 65° C. Based on the soya steamer distillate used, 40 to 80%methanol (preferably 50 to 60%) and 0.8 to 1.5% catalyst (preferably 1%)were used. Sodium methylate was preferably used as the catalyst,although other basic catalysts, for example sodium, potassium andlithium hydroxide, etc., may also be used. The reaction time was approx.2 h at 65° C. After the transesterification, at least 90% of the sterolesters and at least 95% of the glycerides had been reached.

Part B

A pre-esterified deodorizer distillate (pre-esterified with2-ethylhexanol) was charged to a reactor along with 1.5% (by weight ofthe pre-esterified distillate) sodium methoxide and 50% (by weight ofthe pre-esterified distillate) of methanol. The reactor was slightlypressurized to maintain a reaction temperature of 90°. After two hoursof reaction, 90% of the sterol esters present in the distillate feedwere converted to free sterols. The catalyst was neutralized and thesoaps were split by the addition of sulfuric acid (at 98% purity). Themethanol and 2-ethylhexanol were then distilled. The recovered methanolwas 98% pure with 1.5% 2-ethylhexanol and the recovered 2-ethylhexanolcontained 2.6% methanol and was 01.5% pure. The bottoms were then washedwith water until the bottoms exhibited a pH of about 6.

Example 3

Transesterification of the glycerides and sterol esters

2.8 kg deacidified soya steamer distillate, acid value 1.9, werecontacted with 1.4 kg methanol in which 192 g 30% methanolic sodiummethylate had been dissolved. The mixture was heated with continuousstirring to 65° C. and was kept at that temperature for 2 h. To avoidlosses of tocopherol, a nitrogen atmosphere was established.

The starting mixture contained approximately 6% free sterols, a value of16% being determined after transesterification following removal of themethanol component. The initial glyceride content of 25% fell to 1.2%.90% of the glycerides were monoglycerides. Triglycerides could no longerbe detected.

Example 4

Removal of the excess methanol and separation of catalyst and glycerol

After the transesterification, the excess methanol was distilled offfrom the reaction mixture at a temperature of 90° C./1 00 mbar.

The demethanolized reaction mixture contained the catalyst used mainlyin the form of the alkali metal soap. To remove the catalyst from thesteamer distillate, 2.2 kg demethanolized soya steamer distillate wereacidified with 148 g 3% hydrochloric acid and washed with 1.1 kg water.Both phases were separated in a decanter.

Example 5

Separation of the methyl ester

After distillation of the methyl ester formed from the product ofExample 4, a mixture containing 40 Ma % free sterols and 30 Ma%tocopherols was obtained.

Example 6

Part A

Distillation with Packed Column and Wiped Film Evaporator

A distillation apparatus comprised of a packed column and a wiped filmevaporator were employed to distill methyl fatty acids ester from amixture thereof with tocopherols and sterols (at 60.3%, 8.2%, and 9.5%by weight of the mixture, respectively). The column was packed with 3.6meters of wire mesh packing (Montz BSH 400) and had a diameter of 316 mm(to provide eight theoretical stages above the midpoint and eightbelow). A line from the bottom of the column ran to a feed port of awiped film evaporator with an evaporator surface of 1 sq. meter. A linefrom the top of the column ran to a condenser. A feed mixture at 138° C.was fed at 30 kg per hour to the midpoint of the column. The column wasoperated with a pressure and temperature at the top of the column of136° C. and 1.6 mbar, a pressure and temperature at the bottom of thecolumn of 200° C. and 6.6 mbar with a reflux ratio of 0.5 and adistillate per feed of 70.7%. The wiped film evaporator acted as areboiler for the column with the reboiler temperature of 260° C. and apressure of about 1 mbar.

The distillate was 97.0% methyl fatty acid esters and contained nomeasurable levels of tocopherols or sterols. The bottoms from the wipedfilm evaporator were 28.1% tocopherols, 31.5% sterols and 0.2% methylfatty esters which represented a yield of tocopherols of 100% and ayield of sterols of 97.1%. This distillation apparatus could be modifiedby the addition of a falling film evaporator, operated at a lowertemperature than the packed column, e.g. 150° C. and 1.5 mbar, topre-distill approximately half of the methyl fatty acid esters, thebottoms of which are then fed to the packed column.

Parts

Partial Stripping with Wiped Film Evaporator

A pre-esterified, transesterified deodorizer distillate is thricedistilled as follows. The feed is introduced to a wiped film evaporatorwith the heat exchanger surface heated to 170° C. and with an operatingpressure of about 1 mbar. The residence time is adjusted in relation tothe reduced pressure to provide 13% by weight of the feed as distillate.The bottoms are once again fed to the wiped film evaporator, but theheat exchanger surface is heated to 190° C. and the residence time isadjusted in relation to the reduced pressure to provide 19% by weight ofthe feed as distillate. The bottoms are fed for a third time to thewiped film evaporator, but the heat exchanger is heated to 210° C. andthe residence time is adjusted in relation to the reduced pressure toprovide 12% by weight of the feed as distillate. Overall, about 45% byweight of the feed should be removed as distillate.

Example 7

Crystallization of Sterols

The procedure of tests to study the crystallization of sterols is asfollows. We made a mixture of two parts tocopherols (T-130 from HenkelCorporation, Kankakee, Ill.) and one part sterols (Generol 100 fromHenkel Corporation, Kankakee, Ill.) by adding the two in a largecontainer and heating until consistent. We kept this mixture in an ovenat approximately 70° C. to keep it liquid. We filled three 600 mLbeakers with 300 grams of the solvent to be used. To the solvent, weadded 75 grams of the mixture and stirred. One beaker was kept at roomtemperature (approximately 21° C.), one was kept in a refrigerator (-2°C.), and the third was kept in a freezer (-23° C.). These sat overnight,approximately 15 to 20 hours. After the hold time, we assembled a vacuumfiltration apparatus by hooking up a 1000 mL filter flask to anaspirator vacuum source. We placed a Buchner funnel with #1 QualitativeWhatman filter paper on top of the flask and wetted the filter paperwith the solvent. We filtered the solvent containing the mixture throughthis apparatus until all liquid had drained through the paper. Whilefiltering, we placed a nitrogen blanket over the funnel so that theoxygen in the atmosphere did not react with the filter cake. After thefiltration was complete, we placed the filter cake in a baking dish andheated in a vacuum oven overnight to remove any remaining solvent. Wetransferred the mother liquor to a 1000 mL round-bottom flask andstripped it with a roto-evaporator.

Example 7A--Hexane

The procedure set forth above was run employing hexane as the solvent.We noticed the formation of bright white crystals at all temperaturesand a quick filter time. The procedure was twice repeated, employinghexane with methanol/water (1:1 ratio) at a 1% concentration and a 4%concentration, respectively. The procedure was twice repeated again withpure hexane, but at solvent to feed ratios of 3:1 and 2:1, respectively.

Example 7B--Heptane

The procedure set forth above was run employing heptane as the solvent.We noticed the formation of fluffy off-white crystals at alltemperatures. Cold filter time was much slower.

Example 7C--Octane

The procedure set forth above was run employing octane as the solvent.We noticed the formation of fluffy off-white crystals at alltemperatures. Cold filter time was much slower.

Example 7D--Trimethylpentane

The procedure set forth above was run employing trimethylpentane as thesolvent. We noticed the precipitate settled on the bottom and althoughit began as tan, it became bright white at all temperatures.

Example 7E--Cyclohexane

The procedure set forth above was run employing cyclohexane as thesolvent. We noticed a small amount of off-white cake at all temperaturesand a minimal filter time.

Example 7F--Methylcyclohexane

The procedure set forth above was run employing methylcyclohexane as thesolvent. We noticed no precipitate at room temperature and a smallamount at colder temperatures. Filter time was minimal.

Example 7G--Methanol

The procedure set forth above was run employing methanol as the solvent.We noticed a thick slurry of a tan solution with bulky tan precipitateat all temperatures and a minimal filter time.

Example 7H--Isopropanol

The procedure set forth above was run employing isopropanol as thesolvent. We noticed a very dark solution and the precipitate increaseddramatically with lower temperature. Filter time was 15 to 25 minutes.The procedure was twice repeated, employing isopropanol withmethanol/water (1:1 ratio) at a 4% concentration and a 8% concentration,respectively.

Example 7I--Benzyl Alcohol

The procedure set forth above was run employing benzyl alcohol as thesolvent. We noticed precipitate suspended in the solvent at alltemperatures. The boiling point was high and the filter time was greaterthan 15 minutes.

Example 7J--Acetone

The procedure set forth above was run employing acetone as the solvent.We noticed large crystals settled on the bottom at all temperatures anda minimal filter time. The procedure was twice repeated, employingacetone with methanol/water (1:1 ratio) at a 4% concentration and a 8%concentration, respectively. The procedure was twice repeated again withpure acetone, but at solvent to feed ratios of 3:1 and 2:1,respectively.

Example 7K--Methyl Ethyl Ketone

The procedure set forth above was run employing methyl ethyl ketone asthe solvent. We noticed opaque, white, well-defined crystals at alltemperatures and a minimal filter time.

Example 7L--Formic Acid

The procedure set forth above was run employing formic acid as thesolvent. We noticed an extremely dense solution at all temperatures andthe tocopherol/sterol mixture would not dissolve.

Example 7M--Acetic Acid

The procedure set forth above was run employing acetic acid as thesolvent. We noticed ivory precipitate at room temperature and at coldertemperatures the solution was frozen.

Example 7N--Ethyl Formate

The procedure set forth above was run employing ethyl formate as thesolvent. We noticed well-defined, off-white crystals at all temperaturesand a minimal filter time.

Example 7O--Ethyl Acetate

The procedure set forth above was run employing ethyl acetate as thesolvent. We noticed well-defined, off-white crystals at all temperaturesand a minimal filter time.

Example 7P--Dichloroethane

The procedure set forth above was run employing dichloroethane as thesolvent. We noticed flaky tan crystals and the filter time was 15-25minutes. The procedure was twice repeated, employing dichloroethane withmethane/water (1:1 ratio) at a 1% concentration and a 4% concentration,respectively.

Example 7Q--Tetrahydrofuran

The procedure set forth above was run employing tetrahydrofuran as thesolvent. We noticed no precipitate formed at any of the threetemperatures.

Example 7R--Methyl Tetrahydrofuran

The procedure set forth above was run employing methyl tetrahydrofuranas the solvent. We noticed no precipitate formed at -23° C., so no othertests were tried.

Example 7S--Acetonitrile

The procedure set forth above was run employing acetonitrile as thesolvent. We noticed the tocopherol/sterol mixture did not dissolve inthe solvent at any temperature.

Example 7T--Toluene

The procedure set forth above was run employing toluene as the solvent.We noticed a small amount of precipitate in dark solution at alltemperatures and a minimal filter time.

Example 7U--Cyclohexane

The procedure set forth above was run employing cyclohexane as thesolvent. We noticed a large increase in precipitate at the coldertemperatures.

Example 7V--Petroleum Ether

The procedure set forth above was run employing petroleum ether as thesolvent. We noticed no precipitate at room temperature, a smaller amountat colder temperatures and a minimal filter time.

Example 8

Three types of crystallization processes can advantageously be used tocrystallized sterols from admixture with tocopherol. The most simpleprocess is type 1. In this process, no back flow of product isnecessary. The washing liquor is combined with the mother liquor of thecrystallization step. For higher purity of the mother liquor, it issuitable to lead the washing liquor back to the dissolving step like inprocess type 2. Compared to type 1 in this process, a larger amount ofmaterial has to be cooled and crystallized. A process following thescheme of type 3 is a two-stage process. The washed filter cake from thefirst crystallization step is the sterol rich product. The mother liquoris cooled to a lower temperature in a second crystallizer in order toincrease the tocopherol concentration and to minimize the content ofsterols. The remaining mother liquor after this second crystallizationis the tocopherol rich fraction. The washing liquor from the crystals ofthe first stage and the crystals of the second-stage are recycled to thedissolving step. This two-step process is the most complicated becauseof the two crystallizers, the two solid-liquid separators and the amountof product which has to be recycled.

According to the above described processes, three types of experimentscan be carried out.

Type 1: Dissolving the feed materials (boiling under reflux), coolingthe mixture to the final temperature with a constant or the maximumpossible cooling rate, filtering the mother liquor (if necessary themother liquid is refilled into the vessel in order to clean it andfilter it again), washing the filter cake with solvent, combining thewashing liquor with the mother liquor.

Type 2: Same steps as type 1, but keeping the washing liquor and themother liquor apart.

Type 3: Same steps as type 2, but additional cooling of the motherliquor to a lower temperature and a second filtration in order tominimize the amount of sterols in the mother liquor (two-stage-process).

A particular setup that can be employed consists of two stirred 0.5liter vessels with condensers for the dissolving step, a unit forheating and cooling the vessels and a temperated suction funnel combinedwith a filter flask for the filtration step. The solution can be cooledwith a constant rate between 2.5 and 10° C./h or fast cooling rate canbe used. This fast rate covers a range from 80 to 120° C./h, but theaverage value of the cooling rate can depend strongly on the desiredfinal temperature. A lower limit of what is considered fast can be 20°C./h.

In type 1 and 2 experiments, 60 g, and in type 3 experiments, 90 g canbe used as feed. For the washing of the filter cake, 100 g of solventcan be used.

All mother and washing liquors can be stripped in a roto-evaporatoruntil the mass of each is constant. The filter cakes can be placed in abaking dish and heated in an oven up to 75° C. until dry.

A summary of solvents, process types and conditions are shown in thefollowing tables wherein solvent ratio (SR) is based on the mass of thesolvent to the mass of the feed and the process types are as describedabove, but modified according to the following key:

a: without washing the filter cake

b: without stirring

c: liquid trickling out of the filter cake

d: washing the filter cake in suspension

e: recrystallization of the filter cake.

In the following tables, the abbreviation "Meth" indicates methanol as aco-solvent at the weight % indicated. The abbreviation "syn" refers totocopherol/sterol feed prepared by mixing commercially availabletocopherol and sterol. The abbreviation "PTD" refers to atocopherol/sterol feed prepared from a deodorizer distillate bypre-esterification, followed by transesterification, followed bydistillation of the alkyl fatty acid esters. The abbreviation "ML" meansthat the feed was mother liquor from the immediately precedingexperiment (denoted by the experiment number following the abbreviationML). The abbreviation "Ty." refers to the experiment types describedabove.

                  TABLE 1A                                                        ______________________________________                                        STEROL CRYSTALLIZATION WITH ACETONE                                                       Meth    Water      Cooling                                                                             Temp.  Feed                              No.  Ty.    (wt. %) (wt. %)                                                                             S R  Condition                                                                           (fin.) °C.                                                                    Material                          ______________________________________                                        1    1.sup.b                                                                              0       0     4    5° C./h                                                                      0.5    syn                               2    1      0       0     4    5° C./h                                                                      0.0    syn                               3    1.sup.b                                                                              0       0     4    5° C./h                                                                      -15.0  syn                               4    1      0       0     4    fast  -17.2  syn                               5    1      0       0     4    5° C./h                                                                      -20.1  syn                               6    1      0       0     4    fast  -20.8  syn                               7    1      0       0     3    fast  -15.5  syn                               8    1      0       0     3    fast  -17.2  syn                               9    1      0       2     4    fast  -17.0  syn                               10   1      0       4     4    fast  -20.8  syn                               11   1      0       7     4.9  5° C./h                                                                      0.0    syn                               12   1      2       0     4    fast  -19.0  syn                               13   1      2       2     4    fast  -18.0  syn                               14   1      2       2     4    fast  -21.5  syn                               15   2      2       4     4    fast  -17.0  syn                               16   1      4       0     4    fast  -18.0  syn                               17   1      4       0     4    fast  -20.8  syn                               18   1      4       2     4    fast  -15.5  syn                               19   1      4       2     4    fast  -16.0  syn                               20   2      4       2     3    fast  -17.0  syn                               21   1.sup.b                                                                              4       4     4    5° C./h                                                                      1.5    syn                               22   1      4       4     4    5° C./h                                                                      0.0    syn                               23   1.sup.b                                                                              4       4     4    5° C./h                                                                      -6.0   syn                               24   1      4       4     4    5° C./h                                                                      -19.6  syn                               25   1      8       2     4    fast  -17.0  syn                               ______________________________________                                    

                  TABLE 1B                                                        ______________________________________                                        STEROL CRYSTALLIZATION WITH ACETONE                                                       Meth    Water      Cooling                                                                             Temp.  Feed                              No.  Ty.    (wt. %) (wt. %)                                                                             SR   Conditions                                                                          (fin.) °C.                                                                    Material                          ______________________________________                                        26   3.sup.a                                                                              0       0     4    fast  10.2   syn                               27   3.sup.a                                                                              0       0     4    fast  -17.9  ML 26                             28   3      2       0     4    fast  0.0    syn                               29   3.sup.a                                                                              2       0     4    fast  -15.4  ML 28                             30   3      4       4     4    fast  5.0    syn                               31   3.sup.a                                                                              4       4     4    fast  -17.0  ML 30                             32   2      0       0     4    fast  10.0   PTD                               33   2      0       0     4    fast  -18.0  PTD                               34   2      0       2     4    fast  10.0   PTD                               35   2.sup.d                                                                              2       2     4    fast  10.0   PTD                               36   2.sup.d                                                                              4       0     4    fast  10.0   PTD                               37   2      4       0     4    fast  -17.0  PTD                               38   2.sup.e                                                                              4       2     4    fast  10.0   PTD                               39   2.sup.e                                                                              4       2     4    fast  10.0   PTD                               40   2      4       2     4    fast  -17.0  PTD                               41   2      4       2     3    fast  -17.0  PTD                               42   3      2       2     4    fast  9.0    PTD                               43   3.sup.a                                                                              2       2     4    fast  -10.0  ML 42                             44   3      4       4     4    fast  5.0    PTD                               45   3.sup.a                                                                              4       4     4    fast  -14.1  ML 44                             ______________________________________                                    

                  TABLE 2A                                                        ______________________________________                                        STEROL CRYSTALLIZATION WITH ETHYL ACETATE                                                 Meth    Water      Cooling                                                                             Temp.  Feed                              No.  Ty.    (wt. %) (w/. %)                                                                             SR   Conditions                                                                          (fin.) °C.                                                                    Material                          ______________________________________                                        46   1.sup.d                                                                              0       0     4    5° C./h                                                                      0.0    syn                               47   1      0       0     4    5° C./h                                                                      -16.9  syn                               48   1      0       2     4    fast  7.0    syn                               49   1.sup.d                                                                              0       4     4    fast  -17.0  syn                               50   1      2       0     4    fast  0.0    syn                               51   1      2       2     4    5° C./h                                                                      0.0    syn                               52   1      2       2     4    fast  -4.0   syn                               53   1      2       2     4    fast  -15.6  syn                               54   1      2       2     4    5° C./h                                                                      -17.5  syn                               55   1.sup.d                                                                              2       2     3    fast  -17.0  syn                               56   1      4       0     4    fast  -17.0  syn                               57   1      4       0     4    fast  -17.0  syn                               58   1      4       0     3    fast  -17.0  syn                               59   2      4       2     4    fast  -18.0  syn                               60   1      4       4     4    fast  -4.0   syn                               61   1      4       4     4    fast  -16.8  syn                               62   1      4       4     2    fast  -17.0  syn                               63   2      6       4     4    fast  -18.0  syn                               ______________________________________                                    

                  TABLE 2B                                                        ______________________________________                                        STEROL CRYSTALLIZATION WITH ETHYL ACETATE                                                 Meth    Water      Cooling                                                                             Temp.  Feed                              No.  Ty.    (wt. %) (wt. %)                                                                             SR   Conditions                                                                          (fin.) °C.                                                                    Material                          ______________________________________                                        64   3      2       2     4    fast  0.0    syn                               65   3.sup.a                                                                              2       2     4    fast  -18.0  ML 64                             66   3      4       0     4    fast  2.0    syn                               67   3.sup.d                                                                              4       0     4    fast  -17.0  ML 66                             68   2      0       0     4    fast  -10.0  PTD                               69   2      1       1     4    fast  -10.0  PTD                               70   2      2       2     4    fast  -10.0  PTD                               71   2      4       0     4    fast  -10.0  PTD                               72   2.sup.e                                                                              6       4     4    fast  10.0   PTD                               73   2.sup.a                                                                              6       4     4    fast  10.0   PTD                               74   3      2       2     4    fast  5.0    PTD                               75   3.sup.a                                                                              2       2     4    fast  -10.0  ML 74                             ______________________________________                                    

                                      TABLE 3A                                    __________________________________________________________________________    STEROL CRYSTALLIZATION WITH ISO-OCTANE                                               Meth Water   Cooling                                                                              Temp. Feed                                         No. Ty.                                                                              (wt. %)                                                                            (wT. %)                                                                            SR Conditions                                                                           (fin.) °C.                                                                   Material                                     __________________________________________________________________________    76  1  0    0    4  2.5/10° C./h                                                                  10.0  syn                                          77  1  0    0    4  5° C./h                                                                       0.0   syn                                          78  1  0    0    4  fast   0.0   syn                                          79  1  0    0    4  2.5/10° C./h                                                                  -16.7 syn                                          80  1  0    0    4  5° C./h                                                                       -17.2 syn                                          81  1  0    4    4  2.5/10° C./h                                                                  10.0  syn                                          82  1  1    1    4  fast   0.0   syn                                          83  1  1.7  1.7  4  5° C./h                                                                       0.0   syn                                          84  2  2    1    4  fast   -18.0 syn                                          85  1  4    0    4  2.5/10° C./h                                                                  10.0  syn                                          86  1  4    0    4  fast   0.0   syn                                          87  1  4    0    4  5° C./h                                                                       0.0   syn                                          88  1  4    0    4  2.5/10° C/h                                                                   -16.9 syn                                          89  1  4    0    4  5° C./h                                                                       -17.7 syn                                          90  2  4    2    4  fast   -18.0 syn                                          91  1  6    2    4  2.5/10° C/h                                                                   10.0  syn                                          92  1  6    2    4  5° C./h                                                                       0.    syn                                          93  1  6    2    4  fast   0.0   syn                                          __________________________________________________________________________

                  TABLE 3B                                                        ______________________________________                                        STEROL CRYSTALLIZATION WITH ISO-OCTANE                                                    Meth    Water      Cooling                                                                             Temp.  Feed                              No.  Ty.    (wt. %) (wt. %)                                                                             SR   Conditions                                                                          (fin.) °C.                                                                    Material                          ______________________________________                                        94   3      4       0     4    fast  10.0   syn                               95   3.sup.a                                                                              4       0     4    fast  -16.0  ML 94                             96   3      6       2     4    fast  10.0   syn                               97   3.sup.a                                                                              6       2     4    fast  -17.0  ML 96                             98   2      2       1     4    fast  0.0    PTD                               99   2      4       0     4    fast  0.0    PTD                               100  2.sup.a                                                                              4       0     4    fast  -17.0  PTD                               101  2      6       2     4    fast  0.0    PTD                               102  2      6       2     4    fast  0.0    PTD                               103  2      6       2     4    fast  0.0    PTD                               104  2.sup.a                                                                              6       2     4    fast  -13.0  PTD                               105  3      4       2     4    fast  10.0   PTD                               106  3.sup.a                                                                              4       2     4    fast  -17.0  ML 105                            107  3      6       2     4    fast  9.0    PTD                               108  3.sup.a                                                                              6       2     4    fast  -13.0  ML 107                            ______________________________________                                    

What is claimed is:
 1. A method of separating one or more tocopherolcompounds from one or more sterol compounds comprising:dispersing amixture of one or more tocopherol compounds and one or more sterolcompounds, said mixture being essentially free of higher fatty acidcompounds, in a solvent mixture comprised of a major amount of a lowpolarity solvent, said low polarity organic solvent being selected fromthe group consisting of organic hydrocarbon solvents and oxygenatedorganic hydrocarbon solvents, and a minor amount of a high polarityorganic solvent, maintaining the resulting dispersion at a reducedtemperature to produce a liquid phase enriched in tocopherol compoundsand a solid phase enriched in sterol compounds, and separating saidliquid phase enriched in tocopherol compounds from said solid phaseenriched in said sterol compounds.
 2. A process of claim 1 wherein saidlow polarity organic solvent is selected from the group consisting ofhigher alkanes, mono-ketones, mono-aldehydes, mono-esters, and highermono-hydric alcohols.
 3. A process of claim 2 wherein said low polarityorganic solvent is selected from the group consisting of straight-chainor branched chain alkanes having 6 to 12 carbon atoms.
 4. A process ofclaim 2 wherein said low polarity organic solvent is selected from thegroup consisting of n-hexane, iso-octane, acetone, ethyl acetate,isopropanol, and n-butanol.
 5. A process of claim 2 wherein said solventmixture further comprises a minor amount of water.
 6. A process of claim2 wherein said solvent mixture is comprised of from about 80% to about99% by weight of a member selected from the group consisting of higheralkanes, mono-ketones, mono-aldehydes, mono-esters, and highermonohydric alcohols, from about 0.5% to about 20% of methanol orethanol, and from about 0.5% to about 5% by weight of water.
 7. Aprocess of claim 1 further comprising, prior to said dispersing,esterifying with an alcohol fatty compounds in a mixture comprised offatty acids, fatty glycerides, tocopherols and sterols, distilling atleast a major proportion of the fatty acid alkyl esters produced by saidesterifying to produce said mixture of one or more tocopherol compoundsand one or more sterol compounds.
 8. A process of claim 7 wherein saidlow polarity hydrocarbon solvent is selected from the group consistingof higher alkanes.